In an electronic system such as a computer network switch, a backplane is used to provide interconnection between modules of the system. The backplane provides for power distribution and data transport among modules in the system. The backplane includes rows of connectors, which define physical slots, into which the modules are inserted. The modules include at least one connector or a set of electrical contacts along an edge of the module which mate with a corresponding connector on the backplane when the module is inserted into the respective connector on the backplane. The backplane contains signal paths, typically in the form of printed circuit lines for interconnecting the connectors to each other, usually as a bus in which a signal path connects a contact in each connector across the backplane. In a system in which a majority of the signals are bussed, the signal must traverse the entire length of the signal path defining the bus, which often lead to relatively long signal path. Such long signal path lengths are undesirable since they introduce propagation delays into the signal path which can limit the processing speed of the computer system. Propagation delays can be a significant factor in the processing speeds which are obtainable in an electronic system. Additionally, signal transmission characteristics such as reflection, noise and cross-talk also are adversely effected by long signal lengths and considerable caution needs to be exercised in the design of systems employing bussed signal paths to avoid such problems. Such concerns and problems often result in increased cost dedicated to the elimination of such problems during the design of such systems and increased debugging time when problems are detected.
An additional drawback with systems using bussed backplane signal lines is the effect such a bus can experience from "hot swapping" of modules. Hot swapping refers to the ability to remove a module from a system or to insert a module into a system without powering down the system before such insertion or removal. In bussed backplane systems, hot swapping of modules can negatively effect other modules of the system. Since the bussed signal line is in common with the other modules connected to the bus, removing or adding a module to the bus while the system is powered on results in the bussed signal characteristics being changed, which in turn affects the signal being transported along the bussed signal line.
It would be desirable to provide a high speed interconnect between modules of a system that affords substantial improvements in signal speed while maintaining signal integrity with short interconnect transmission lines to ensure fast edge rates, and while permitting hot swapping of modules without impact on other modules which continue to operate within the system.